Lamp



Nov. 7, 1950 F. OF'PENHEIMER LAN? 2 Sheets-Sheet 2 Filed March 7, 1945 Patented Nov. 7, 1950 UNITED STATES PATENT OFFICE LAMP Application March 7, 1945, Serial No. 581,405

Claims.

This invention relates to a lamp emitting irradiation of extreme ultraviolet rays in the Schumann range of an intensity heretofore unknown and unobtained.

While the electromagnetic spectrum does not have sharply defined zones, arbitrary divisions have been established. Thus, Benjamin M. Duggar, in his book "Biologic Eifects of Radiation, volume I. page 15, defines the subdivisions of the ultraviolet as the zone of transmission by the earths atmosphere" extending from the edge of the violet out to about 2900 A. (4.3 E. v.) at which the atmosphere ceases to transmit and beyond which the spectra of the sun and stars cannot be followed: the Schumann region between the 2000 and 1250 A. (6.4 and 10 a. V.) in which fluorite must be used for the lenses and prisms and special photographic films are necessary; and the Lyman region extending thence to about 500 A. (about 25 E. v.) in which still more exceptional films are requisite and only the thinnest strata of solid matter (or better, none at all) may be put across the light beam. Prior to this invention, lamps of high intensity for the radiation of rays of the Schumann region had never been made. Light sources of the Geissler type were used for spectrographic studies in this region of the spectrum. In a Geissler tube, a gaseous discharge is excited by high voltages, 1000 to 10,000 volts, with a very low current of a few mllliamperes (1-30 milliamperes). The output of energy in the Schumann region is so low (below 1 microwatt per square centimeter) that it can only be used for spectroscopic purposes.

By means of the present invention, emission in the Schumann region may be produced in great intensity. The effects of this energy can be utilized for photochemical and biological studies and processes with results heretofore unobtainable.

Fundamentally, the lamp of the present invention is a gaseous arc discharge, excited by low voltages, and operating at very high current intensities (5 to 50 amperes). It maintains its peculiar spectral characteristics even at an electrical load of 5 kilowatts. An important feature of the invention is the operation of the lamp at a constant low gas or vapor pressure in spite of the high current consumption. While the power characteristics of the lamp are similar to the well-known mercury quartz arc, the spectral emission (energy distribution) is entirely different from the mercury quartz arc spectrum, and is more comparable to the radiation of a quartz Geissler tube, commonly referred to now as cold quartz lamp.

If an arc discharge is excited in mercury vapor of very low pressure, the characteristic resonance spectrum of mercury is emitted. The mercury resonance spectrum has comparatively few lines; most of the ultraviolet energy is concentrated in the lines 2537 A. and 1849 A. Theoretically, under ideal conditions, the energy in the band designated 1849 A. should have an intensity many times greater than that of the line 243': A.

I have found that when a powerful stream of low velocity electrons is directed into mercury vapor of constant low vapor pressure (below 1 millimeter of mercury), the mercury atoms are excited and emit the resonance lines of 2531 A. and 1849 A in great intensity. This phenomenon is not gradually or progressively produced, but is one of sharply defined and threshold conditions. A low, constant vapor pressure, below i millimeter, preferably 1 to 20 microns of mercury within the lamp, is required. As unexcited mercury atoms will absorb the radiation of excited mercury atoms, the less the number of total mercury atoms, the less the probability for self-absorption and resultant self-reversal of the resonance lines. This phenomenon is much more pronounced for band 1849 A. The number of electrons bombarding the mercury vapor must be very great to increase the probability of excltation; this can be expressed simply as a current of high intensity, 5 to 50 amperes. The power factor most favorable for the emission of Schumann rays is high amperage and the lowest possible voltage, and highly emissive cathode will reduce to a minimum the voltage drop from electrode to gas.

The mercury resonance lines, 2537 A and 1849 A can be produced as true monochromatic radiation by means of a device described in Ellis and Wells The Chemical Action of Ultraviolet Rays, page 8. In this device, an electron stream thermionically-produced and accelerated by passing it through a screen of a constant fixed voltage bombards the mercury vapor. At 4.9

volts, a single line with a wave length of 2537 A.

appears; at 6.7 volts, one with a wave length of 1849 A. is produced. These voltages are called electron-volts or absolute volts. There is a definite relationship between these voltages and the frequency of the emitted wave lengths. This can be calculated by dividing the energy by a fundamental natural constant, the quantum of action or Planck's constant. These truly monochromatic sources of radiation are very weak in intensity and only of theoretic value, but it is evident from a study of this device that for a light source designed to produce 1849 A. in very high intensity a voltage level should be chosen for a mercury vapor arc discharge which insures the probability that a. large percentage of the electrons bombarding the mercury atoms is accelerated by a voltage of 6.7 volts.

I have discovered that a mercury arc discharge tube of considerable length (50 cm. or more disstance between electrodes) can be operated in very high vacuums of l to 20 microns, at 40 to 80 volts and at high current intensities of 5 to 50 amperes. This operation produces the conditions corresponding to a true monochromator. Improvements and refinements were directed to two purposes: first to secure the optimum radiation of 1849 A. and second, to find practical means of passing this radiation through the envelope of the arc discharge tube. Important requirements for intense radiation of 1849 A. are a highly emissive cathode to produce a very large stream of electrons, and means to keep the mercury vapor pressure in the tube at a constant low level not exceeding 1 millimeter, and preferably not exceeding 20 microns. The mercury vapor pressure in the tube is not uniform. The large amount of heat generated at the electrodes, especially the anode, must be removed instantaneously. otherwise it would greatly increase the vapor pressure in the lamp. This heat is produced through the intense electronic bombardment of the anode and the ionized atomic bombardment of the cathode. In a lamp containing liquid mercury, the partial pressure of mercury is determined by the temperature of the coldest point if the area of the coldest point is large enough and suflicient cooling is provided to remove heat rapidly and efllciently. Restrictions in the system should be avoided, otherwise great differences in vapor pressure might occur. A lamp of this character reaches an equilibrium for its operating conditions. In a mercury are discharge tube with solid electrodes, a low constant mercury vapor pressure in the tube can be achieved by distilling into the lamp 9. measured amount of liquid mercury calculated to give the desired mercury vapor pressure when the liquid mercury vaporized at the operating temperature of the lamp. A serious fault to this method is that the mercury might be gradually absorbed by the solid electrodes and lead-in wires so that the mercury is gradually removed from the system until eventually there is no active mercury left. A new and novel method of maintaining a constant low vapor pressure in an arc discharge tube has been accomplished the following way. A liquid cooled vessel which can be kept at a constant temperature and containing a small amount of amalgam (such as an amalgam of silver or gold or other metal of low vapor pressure) is connected to the lamp. The concentration of mercury in the amalgam and the temperature at which it is kept will determine the exact absolute mercury vapor pressure in the system.

Radiation of a wave length shorter than 2000 A. is readily absorbed by most substances. Fluorspar and spinal have a very low absorption factor, but their use is impractical as it is not radiation tube as it makes a vacuum-tight lamp envelope. Quartz has a much greater absorption for the band designated at 1849 A. than iluorspar, but if the irradiation tube is made from very pure optical quartz of a thickness not exceeding /2 mm.. the loss of this radiation by absorption in the envelope is not significant due to the very intense emission produced in this band by the lamp of the present invention. The literature has many contradictory statements and claims on the light permeability properties of various substances used as envelopes. By our measurements. we have estabiished that pure optical quartz of 0.5 millimeter thickness absorbs less than 5 percent of 2537 A. and about 10 percent of 1849 A. Corning glass, No. 791 (96% S102) optically clear and l millimeter thick, totally absorbs the 1849 A. band and absorbs 15 percent of 253': A. Corex D glass, No. 9700, in 2 millimeter thickness. totally absorbs 1849 A. and over of 253': A. At the present time, therefore, only very thin optically pure quartz is a feasible envelope for a lamp from which it is desired to obtain Schumann rays of any quantity.

The lamp of the present invention produces radiation of wave length 1849 A. in an intensity as high as 20 milliwatts per cm. This measurement was performed by exposing 1 cm. length of the irradiation tube, which is 12 to 16 mm. in diameter, at a distance of 1 cm. from a standardized balanced thermopile, and the difl'erentiation between wave lengths 1849 A. and 2637 A. calibrated by means of standard filters. The short distance between lamp and meter has to be chosen because radiation shorter than 2000 A. is readily absorbed by air with the resulting production of ozone and nitrous oxides. We have measured this absortpion and have found that approximately 50 percent of the energy of the 1s 49 A. band is absorbed in 10 cm. of air. The present lamp, burning in' air, produces a great deal of ozone. and the measurements of the thermopile have been checked by measuring the ozone production of the lamp. These measurements show a good correlation within the limit of experimental error. The measurements of the lamps referred to later are made under the conditions described above.

As a standard for. a cold quartz lamp, I employed a 80-2537 Raman Eifect quartz tube manufactured by the Hanovia Company, operating from a transformer rated at milliamperes at 6000 volts. This cold quartz lamp burns at a lamp voltage of 395 volts and a current of approximately 40 milliamperes. The total ultraviolet radiation of this lamp, of which 95% is concentrated in band designated 2537 L, measured at a distance of 1 meter is 40 microwatts per cm.', exposing approximately 60 cm. of irradiation tube. Comparative studies with the present lamp and the standard cold quartz lamp showed the following results. The above described method of measurement was utilized. One cm. length of the irradiation tube was exposed to a compensated thermopile at a distance of 1 cm.. and for differentiation, calibrated filters were used. The lamp of the present invention produces a total ultraviolet output of approximately milliwatts per cm. per second. of which approximately 20 to 30 miiliwatts per cm. are radiated as 1849 A. The sc-zssv radiates approximately 1 milliwatt per cm. total ultraviolet measured at 1 cm. distance, of which only ap;

- proximately 2 microwatts are radiated as 1849 A.

asaaooo Adeterminationoitheoaoneproductionbythe two lamps shows a good comparative check.

whenextrapolatedtoonemeterdistaneethe outputoienergyotthelampoithepresent energy between 2000 L. and 2000 A. is a little more than 1 milliwatt. in contrast to the energy output of the cold quartz lamp measured at the same distance, which is 40 microwatts, between zmfiandmlaandpractlh nllbelow 2000 Inthedrawingslhaveshown one embodiment of the invention. In this show- Figllsaditicviewoioneiormoi lamp constructed in accordance with the invention:

Fig. 2 is a similar view of another form 01' lamp provided with solid electrodes;

Fig. 3 is a ditic view of another form oi lamp constructed in accordance with the invention; and

Fig. 4 is a diagrammatic view of a starting device.

Referring to Fig. 1 the lamp comprises a pair of electrode chambers I and 2 in each of which is provided a mercury pool 3 and 4. The mercury pool is approximately 1 cm. deep. The electrode chamber may be substantially millimeters in diameter and 25 cm. long. A platinum tipped lead-in wire 5 extends through a suitable seal 6 into each of the mercury pools. A water jacket I surrounds the electrode chamber, the water jacket being provided with an inlet 8 and an outlet 9. The irradiation tube i0 is sealed to the electrode chambers by a quartz connecting tube H. The two ends of the lamp may be connected to each other by a brace 12 for strengthening purposes.

The tube forming the electrode chamber is very thin to permit good heat transfer. The liquid mercury cathode is capable oi emitting a large stream of electrons, and being in close contact with the cooling liquid in the water jacket 1 its temperature will not rise appreciably. The mean mercury pressure in the lamp should not rise above 1 millimeter and is preferably below microns. The lower and more constant this pressure can be maintained, the better and more intense is the output of the extreme ultraviolet radiation. The anode must likewise be cooled because a great deal of heat is created by the massive electronic bombardment.

The irradiation tube II is formed of pure optical quartz having a very thin wall, less than mm. thick. It may have an inside diameter of 10 to 20 mm. and may be of any desired length. In constructing the lamp, it is first evacuated to a very high vacuum, not over .001 micron pressure. The lamp body is first baked in an oven at a temperature of 600 to 700 C. and connected to a mercury diffusion pump with several liquid air traps to insure the removal of all traces of moisture. Water, being a good catalyst, will facilitate chemical reaction between the quartz and the mercury under the influence of intense electron bombardment. This would result in the formation of mercury silicates which are opaque to the radiation of 1849 A.

After the lamp has been thoroughly baked and exhausted spectral pure mercury is distilled into the lamp. In order to remove minute quantities of water which may be present in the mercury. the mercury vapor is passed through a mercury a dischargebetweentwoliquidcooledmercuryeleetrodes belore entering the lamp.

Alampoithischaracterwilloperate atacurrentofiiltodilveltsandfitowormoreamperes. The voltage for operating the lamp depends essentially on the two iactors, cathode emissivity and vapor pressure. As stated before, a highly emissive cathode reduces the voltage drop from electrode to gas. At a ilxed or desired wattage, the lamp will operate on a voltage which falls proportionally with the d internal vaporpressureuntilthatpressurereachesso low a point that the mean free path is lengthcued, at which time in voltage will be required. Thus, a lamp oi amereury vapor pressure at 1 millimeter might operate at 120 volts and 10 amperes for 1200 watts. On the other hand, it the mercury vapor pressure is around 50 microns, the operating voltage would be reduced to volts for 1200 watts with a 20 amperecurrent. Because of the low vapor pressure, the internal resistance oi the lamp'is very low, even with a high operating current. One lamp having a length of 40 cm. has an internal resistance of 4 to 6 ohms. This resistance remains practically constant regardless oi the current input.

The method of cooling the electrodes and electrode chambers is of great importance, both in regard to the temperature of the cooling liquid and the rate or flow. The lamp shown in Fig. 1 produces 20 milliwatts per cm. of extreme ultraviolet radiation at a cooling liquid temperature of +5 6., and a flow through each electrode chamber of 2 liters per minute. Schumann rays in quantity are emitted from a mercury are discharge tube only if the foregoing criticalconditions are strictly observed. It the vapor pressure in the lamp is permitted to rise above 1 millimeter, the emission of 1849 A. sharply declines.

while the radiation oi the band 2537 A. is only slightly diminished. If the temperature oi the cooling liquid should be raised, maintaining the same rate 01 flow to +60 C., the band 1849 A. is reversed in the spectrum emitted by the lamp, even to total disappearance.

In the form oi the invention shown in Fig. 2 the lamp is a straight lamp and solid electrodes are employed. As shown, the lamp comprises a pair of electrode chambers i3 surrounded by water jackets ii. The irradiation tube I5 is connected to each of the electrode chambers by quartz tubing 16. Metal cups I! are sealed directiy into the ends of the electrode chambers as at 18 and lead-in wires I! are connected through these cups. The surface 20 of each of the cups forming the ends of the vacuum tube is made of a metal resistant to mercury. Water cooling for the cups is provided by means of inlets 2i extending into the cups i1 and outlets 22.

In a lamp built in accordance with this disclosure the electrode chambers were 15 cm. lon and of a diameter of 10 mm. The irradiating tube i5 was 15 cm. long and 14 mm. in diameter. The irradiating tube was formed of pure optical clear quartz approximately mm. thick and was connected to the electrode chambers by quartz tubing l8, 15 mm. long. The platinum, or other metal plating, of the electrodes is for the purpose of avoiding the formation oi an amalgam which most metals readily form with mercury. The lamp disclosed in Fig. 2 is prepared and evacuated in the manner described in connection with Fig. l. A minute amount (a few milligrams) of mercury, caesium or other highly emissive elements or compounds, is distilled into the lamp and a small amount of a gas, such as argon or xenon at a pressure of less than 1 mm. is placed in the tube. The latter facilitates starting the lamp. In electronic devices of considerable power, liquid cooled anodes are frequently employed to remove the heat created by electronic bombardment. They have been successful, especially in X-ray tubes. Two types of cathodes are commonly employed for powerful electronic emission. One is the hot oxide coated cathode, such as in power tubes, and'the other type is the mercury pool cathode, such as in large current rectiflers. There are many drawbacks to the hot cathode, especially the sharp limitation imposed by practical working temperatures and sizes upon the electron emission and the fact that the atomic bombardment destroys the oxide coating. Once a discharge has been started from a hot cathode, it is a diflicult problem to remov the heat created by bombardment by positively charged ions. This invention also includes a liquid cooled solid cathode capable of emitting an electron stream of unlimited capacity. Its temperature can be maintained at any desired level within ,narrow limits. Since this electrode temperature can be reduced to any desired level by employing a refrigerated cooling liquid, it is possible to use such coatings as would otherwise volatilize. Not only can the cathode be reduced to any desired temperature, but it can also be made the coldest point in the system. Thus, a, thin film of mercury which emits readily at low temperatures when plated on such a liquid cooled cathode will remain in place and will not evaporate from the cathode surface. Likewise, other readily emitting but volatile substances, such as caesium and many other-compounds, can be utilized for their property of electronic emission.

The lamp operates with the same current characteristics as the lamp disclosed in Fig. 1 and the output of Schumann rays is of the same order. Contrary to past belief the same intensity of electron emission can be effected from this liquid cooled cathode as from a hot cathode. A minute, possibly monomolecular, film of mercury coating on the metal electrode is responsible for the high emissivity of this cathode. The constant cooling retains the film on the surface of the metal. This lamp has many advantages. It has a longer life than the lamp shown in Fig. 1 or the lamp shown in Fig. 4, which is probably due to the small amount of mercury present. The liquid cooling of both electrodes avoids "sputtering which increases the life and emciency of the lamp. The liquid cooled cathode does not deteriorate under the bombardment of positively charged mercury atoms in contrast to the oxide coated hot cathodes commonly used in lamps of this character. The liquid cooled cathode, plated in the manner described, can be employed if the discharge is operated with alternating current. In this case, both electrodes should be of the plated liquid cooled cathode type, and the cooling of the electrode, made according to this invention, is so eflicient that even during the periods when the cathode takes over the functions of the anode, the much greater amount of heat thus created can be rapidly dissipated into the cooling fluid.

In Fig. 3 of the drawings I have disclosed a lamp which is a straight lamp but is otherwise generally similar to the construction shown in Fig. 1. It is provided with electrode chambers 23 and 24 similar to the electrode chambers of 8 Fig. l. The cathode is provided with a pool of liquid mercury 25 to which lead-in wire 26 is connected and a solid electrode, similar to the electrodes of Fig. 2, forms the anode. As shown, cup 2'1 is sealed to the tube 28 of the anode electrode chamber and a lead-in wire 29 is connected to this cup. Each of the electrode chambers is surrounded by a water jacket 28, the water Jackets beingprovided with inlets 30 and outlets 38. The cup is also liquid cooled on the interior. An irradiating tube 32 is connected to the two electrode chambers in the manner heretofore described. This lamp is operated in a vertical position as shown and the straight path provided for the electron stream tends to increase the life of the lamp over that of the lamp shown in Fig. 1 because the electrode bombardment of the quartz irradiating tube is reduced to a minimum. The lamp operates with the same .current characteristics as heretofore described and the output of Schumann rays is of the same order.

Light sources for the Schumann rays designed and constructed in accordance with this invention are difllcult to start. The lamps as shown in Figs. 1 and 3 do not contain a starter as, and with the cooling liquid flowing through the electrode chambers, the total pressure in the lamp is less than 1 micron. I have found a starter gas in the liquid pool type of electrode lamp harmful to the emission of extreme ultraviolet. One method of starting isto disconnect the liquid cooling and pre-heat the mercury pools in the electrode chambers. A Tesla transformer is used to ionize the mercury vapor, and as soon as a discharge starts, the liquid cooling is turned on. Within a few minutes the mercury vapor pres-- sure within the lamp is reduced to the operating pressure of less than 20 microns. A draw back of this method is that great care has to be exercised in heating the mercury pool to the right temperature (corresponding to a mercury vapor pressure between 500 to 2000 microns), because if the mercury is heated too high, the discharge will not start.

The starter shown in Fig. 4 of the drawings has been used successfully with the three lamps shown in Figs. 1 to 3. It consists of a luminous type transformer rated at 10,000 volts and comprising a primary coil 35 and a secondary coil 36. The primary coil is connected to a source of 110 volts alternating current by lead wires 31 and 38. A 10 ohm. resistance 39 is placed in the primary of the transformer to prevent overloading. One side of the secondary oi the transformer is connected to a rectifier tube 40 and the grid of the tube is connected by lead wire ll to the cathode 42 of the lamp 53. A 220 volt D. C. generator M, which is normally used to operate the lamp after starting, has its negative side connected to the cathode through wire 45 and an interposed rectifier tube 48. The tube 46 blocks current from the transformer from entering the D. 0. generator. The other side of the secondary coil 36 is connected through wire 41 to the anode 48 of the lamp and is grounded at 9. A 100.000 ohm rheostat 5B is inserted in this connection. A momentary contact switch 5| is provided in the leads of the primary coil of the transformer and a. knife switch 52 is arranged in one of the leads from the source of alternating current to the filament transformers and 54 of rectifier tubes 40 and 48, respectiveLv. A by-pass 55 is provided in the lead 45 from the negative side of the D. C. generator and a control switch 56 is arranged in this by-pass. Condensers 81 may be arranged between Switch 52 is closed to heat the filaments oi the rectifier tubes 00 and 40. Switch ill, which may be of the push button type, is closed for a fraction of a second permitting fluctuating high voltage, direct current to flow from the transformer to the lamp. With the generator 44 connected 1:;

by the closure of switch 50, switch 56 is then closed to by-pass the rectifier tube 56. As soon as the operation of the lamp continues from the current supplied by the generator 44, switch 52 is opened to disconnect the starting apparatus 2 from the lamp.

While the primary and most important uses of the invention as now known are as a source of ultraviolet radiation of very high intensity for sterilizing purposes, the apparatus may also be used as a high capacity rectifier in the same manner that normal mercury vapor lamps are now employed for that purpose. With the present types of mercury vapor rectiflers, either the cabersome, complex structures when high capacity rectification is desired. High capacity rectification may be obtained by means of the present lamp, the lamp otherwise functioning as present normal types of mercury vapor lamps when used as a rectifier.

I claim:

1. A high intensity, low pressure resonance lamp comprising an irradiation tube substantially unimpeded to the emission of ultraviolet irradiaa tions below 2600 A.. an electrode chamber at each end of the irradiation tube, the walls of the electrode chambers being formed of thin material to permit rapid heat transfer, a highly emissive cathode arranged in one of the electrode chambers, an anode in the other electrode chamber, a cooling jacket surrounding each of the electrode chambers, each oi the cooling jackets being provided with an inlet and an outlet, means for passing a cooling liquid through the cooling jackets, and a quantity of mercury in the lamp in excess -of'that required to fill the lamp with mercury valamp comprising an irradiation tube substantially 65 unimpeded to the emission of ultraviolet irradiations below 2600 A" an electrode chamber at each end of the irradiation tube, the walls of the electrode chambers being formed of thin material to permit rapid heat transfer, a h ghly emissive 70 cathode arranged in one of the electrode chambers, an anode in the other electrode chamber, a cooling jacket surrounding each of the electrode chambers, each of the cooling jackets being provided with an inlet and an outlet, means tor pass- 76 log a cooling liquid through the cooling jackets. and a quantity of mercury in the lamp in' excess of that required to fill the lamp with mercury vapor at 1 mm. pressure, the capacity of the cooling jackets and the cooling means being sumcient to maintain the vapor pressure in the irradiation tube below 1 mm. at a current input of approximately 10 watts per linear centimeter of the lamp and an ultraviolet output below 2600 A. substantially milliwatts per square centimeter, and between 2000 A. and 1500 A. of substantially 1o milliwatts per square centimeter measured at 1 centimeter distance when a liquid at a temperature of 5 C. flows through the jacket at the rate of 2 liters per minute, and in which the irradiation may be substantially increased or decreased proportionately to the increase or decrease of current input.

3. A high intensity, low pressure resonance lamp comprising an irradiation tube substantially unimpeded to the emission of ultraviolet irradiations below 2600 A, an electrode chamber at each end of the irradiation tube, the walls of the electrode chambers being formed of thin material to permit rapid heat transfer, a liquid mercury pool cathode in one of the electrode chambers, an anode in the other electrode chamber, a cooling jacket surrounding each of the electrode champacity is limited or it is necessary to employ cumberseach the coming jackets being Pmvided with an inlet and an outlet, means for passing a cooling liquid through the cooling jackets, and the quantity of mercury in the lamp in excess of that required to fill the lamp with mercury vapor at 1 mm. pressure, the capacity of the cooling jackets and of the cooling means being sufficient to maintain the vapor pressure in the irradiation tube below 1 mm. at a current input of approximately 10 watts per linear centimeter of the lamp and an ultraviolet output below 2600 A. substantially 50 milliwatts per square centimeter measured at l centimeter distance, when a liquid at a temperature of 5" C. flows through the jacket at the rate of 2 liters per minute.

4. A high intensity, low pressure resonance lamp comprising an irradiation tube substantially unimpeded to the emission of ultraviolet irradiations below 2600 5., an electrode chamber at each end of the irradiation tube, the walls of the elecso trode chambers being formed of thin material to permit rapid heat transfer, a liquid mercury pool cathode in one of the electrode chambers, an anode in the other electrode chamber, a cooling jacket surrounding each of the electrode chambars, each of the cooling jackets being provided with an inlet and an outlet, means for passing a cooling liquid through the cooling jackets, and the quantity of mercury in the lamp in excess of that required to iill the lamp with mercury vapor at 1 mm. pressure, the capacity 01' the cooling jackets and of the cooling means being sufiicient to maintain the vapor pressure in the irradiation tube below 1 mm. at a current input of approximately 10 watts per linear centimeter of the lamp and an ultraviolet output below 2600 A, substantially 50 milliwatts per square centimeter, and between 2000 A. and 1500 A. of substantially l0 milliwatts per square centimeter measured at 1 centimeter distance when a liquid at a temperature of 5 C. flows through the jacket at the rate of 2 liters per minute, and in which the irradiation may be substantially increased or decreased proportionately to the increase or decrease of current input.

5. A high intensity, low pressure resonance lamp comprising an irradiation tube substantially unimpeded to the mission 01' ultraviolet irradiations below 2600 A., an electrode chamber at each end of the irradiation tube, the walls of the electrode chambers being formed of thin material to permit rapid heat transfer, a solid metallic cathode having a coating of a highly emissive material in one of the electrode chambers, an anode in the other electrode chamber, a cooling jacket surrounding each of the electrode chambers, each of the cooling jackets being provided with an inlet and an outlet, means for passing a cooling liquid through the cooling jackets, and a quantity of mercury in the lamp in excess 01' that required to fill the lamp with mercury vapor at 1 mm. pressure. the capacity 01' the cooling jackets and of the cooling means being sufficient to maintain the vapor pressure in the irradiation tube below 1 mm. at a current input of approximately 10 watts per linear centimeter of the lamp and an ultraviolet output below 2600 A. substantially 50 milliwatts per square centimeter measured at 1 centimeter distance, when a liquid at a temperature of 5 C. flows through the jacket at the rate of 2 liters per minute.

6. A high intensity. low pressure resonance lamp compris ng an irradiation tube sub tantially unimpeded to the emission of ultraviolet irradiations below 2600 A an electrode chamber at each end of the irradiation tube. the walls of the electrode chambers being formed of th n ma terial to permit rapid heat transfer, a solid metallic cathode having a coating of a highly emissive material in one of the electrode chambers, an anode in the other electrode chamber, a cooling jacket surrounding each of the electrode chambers. each of the cooling jackets being provided with an inlet and an outlet, means for passing a cooling liquid through the cooling jackets, and a quantity of mercury in the lamp in excess of that required to fill the lamp with mercury vapor at 1 mm. pressure, the capacity of the cooling jackets and the cooling means being suil'icient to maintain the vapor pressure in the irradiation tube below 1 mm. at a current input of approximately 10 watts per linear centimeter of the lamp and an ultraviolet output below 2600 A. substantially 50 milliwatts per square centimeter. and between 2000 A. and 1500 A. of substantially l m lliwatts per square centimeter measured at l centimeter distance when a liquid at a tem erature of 5 C. flows through the jacket at the rate of 2 liters per minute. and in which the irradiation may be substantially increased or decreased proportionately to the increase or decrease of current input.

7. A high intensity, low pressure resonance lamp comprising an irradiation tube substantiallv unimpeded to the emission of ultraviolet irradiations below 2600 A" an electrode chamber at each end of the irradiation tube, the walls of the electrode chambers being formed of thin material to permit rapid heat transfer, a highly emis ive cathode comprising a cup-shaped member having the bottom surface of the cup exposed in the tube and coated with a highly emissive material in one of the electrode chambers, an anode in the other electrode chamber. a cooling jacket surrounding each of the electrode chambers, each of the cooling jackets being provided with an inlet and an outlet, means for passing a cooling liquid through the cooling jackets, and a quantity of mercury in the lamp in excess of that required to till the lamp with mercury vapor at 1 mm. pressure, the capacity of the cooling jackets and the cooling means being suflicient to maintain the vapor pressure in the irradiation tube below 1 mm. at a current input of approximately 10 watts per linear centimeter of the lamp and an ultraviolet output below 2600 A. substantially milliwatts per square centimeter measured at 1 centimeter distance, when a liquid at a temperature of 5 C. flows through the jacket at the rate of 2 liters per minute.

8. The method oi producing ultraviolet irradiations lower than 2000 A. of an intensity of substantially 10 milliwatts per square centimeter measured at 1 centimeter distance which comprises pa sing a current of approximately 10 watts per linear centimeter through a lamp com prisin an irradiation tube substantially unimpeded to the emission of such rays, the irradiation tube having electrode chambers at each end, the walls of the electrode chambers being formed of thin material to permit rapid heat transfer, a high y emissive cathode in one of the electrode chambers and an anode in the other e'ectrode chamber. and a quantity oi mercury in the tube in excess of that required to fill the tube with mercury vapor at 1 mm. pressure, and cooling jackets surrounding the electrode chambers, and passing a cooling liquid through the cooling jackets while the lamp is in operation at a rate sufficient to maintain a vapor pressure in the irradiation tube below 1 millimeter in the tube. the capacity oi the cooling jackets and the flow of the cooling liquid being suificient to produce a low internal resistance in the lamp.

9. The method 01' producing ultravio et irradiations lower than 2600 A. 01' an intensity of substantially 50 milliwatts per square centimeter measured at 1 centimeter distance which comprises passing a current of approximately 10 watts per linear centimeter through a lamp comprising an irradiation tube substantially unim peded to the emission of such rays, the irradiation tube having electrode chambers at each end. the walls oi the electrode chamb rs being formed of thin material to permit rapid heat transfer, a highly emissive cathode in one of the electrode chambers and an anode in the other electrode chamber, and cooling jackets surrounding the e ectrode chambers, and a quantity of mercury in the tube in excess oi that required to fill the tube with mercury va or at 1 mm. pressure, and passing a cooling liquid through the cooling jackets while the lamp is in operation at a rate sufllcient to maintain a vapor pre sure below 1 mm. in the tube, the ca acity of the cooling jackets and the flow of cooling liquid being suffieient to produce a low internal resistance in the lamp.

10. A high intensity, low pressure resonance lamp com rising an irradiation tube substantially unimpeded to the emission of ultraviolet irradiations below 2600 A, an e ectrode chamber at each end of the irradiation tube. the walls oi the electrode chambers being formed of thin material to permit ra id heat transfer. a solid metal cathode in one of the el ctrode chambers, the cathode being provided with a coatin of metal that does not readily amalgamate with mercury, an anode in the other electrode chamber, a cooling jacket surrounding each of the electrode chambers, each oi' the cooling jackets being provided with an inlet and an outlet, means for passing a cooling liquid through the cooling I jackets. and a quantity of mercury in the lamp in excess of that required to fill the lamp with mercury vapor at 1 mm. pressure, the capacity 01' the cooling jackets and of the cooling means being sufflcient to maintain the vapor pressure in the irradiation tube below 1 mm. at a current 5 input of approximately 10 watts per linear centimeter of the lamp and an ultraviolet output below 2600 A. substantially 50 milliwatts per square centimeter measured at 1 centimeter distance, when a liquid at a temperature of 50 C. flows through the jacket at the rate of 2 liters per minute.

FRANZ OPPENHEIMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,152,987 Dorgelo Apr. 4, 1939 2,272,486 stacker Feb. 10, 1942 2,278,844 Francis Apr. '7, 1942 2,300,892 Harada Nov. 3, 1942 2,329,125 Lemmers Sept. 7, 1943 2,359,057 Skinner Sept. 26, 1944 2,362,385 Libby Nov. 7, 1944 

